1. Field of the Invention
This invention relates to bonding systems, particular apparatus and methods for forming a bonded structure incorporating a semiconductor layer.
2. Background Information
A layered assembly incorporating a semiconductor wafer is a structure useful for forming devices such as transistors, displays and microelectromechanical systems. A basic step of manufacturing the layered assembly includes bonding a semiconductor wafer to a substrate by, for example, thermo compression, fusion, or anodic bonding.
In order to minimize the nucleation of multiple bonding fronts, and concomitant concentration of voids in the bond, it is desirable to control the development of contact between the opposing bonding faces of the wafer and substrate. Accordingly, in a conventional bonding apparatus, the semiconductor wafer and substrate are first arranged with their respective bonding faces separated across a narrow separation. Commonly the bonding apparatus provides small peripheral spacers that are inserted between the stacked wafer and substrate to keep the bodies separate. After contact between the two facing surfaces has been initiated, the spacers are retracted.
The use of spacers may introduce difficulties into the bonding process. Mechanical contact between the spacers and the bonding surfaces of the two bodies may cause undesirable scratching, contamination, or particle generation and thereby compromise the quality of the bond and the performance of the ultimate device. In more extreme cases, the spacers may become stuck fast between and ruin the two bodies. The spacers may be thin and prone to break, thereby reducing reliability of the bonding apparatus and compromising throughput due to downtime for maintenance. Also, managing the deployment and retraction of the spacers increases the complexity and expense of the bonding apparatus.
There is, accordingly, a need for a bonding system enabling management of contact development between the two bodies being bonded without interposed spacers.